This invention relates to threshold receiver circuits and, specifically, receiver circuits which are process and temperature insensitive.
Numerous types of receiver circuits are found in the prior art, especially those used to receive signals in computer applications. Typically, the circuits receive an analog input signal which, when the input signal is less than a predetermined minimum threshold, will output a first logic signal and when greater than a predetermined maximum threshold, will output a second logic signal. Receiver circuits are known in the prior art which use an input buffer with hysteresis. However, in the prior art circuits both the positive going and negative going thresholds are strongly dependent upon device process parameters and temperature. Also, in order to achieve apparent thresholds which are outside the range of the supply voltages for the receiver circuit, prior art circuits require at least two resistors per input signal. In addition, testing such prior art circuits is difficult when the logic output signal is not directly observable.
The present invention overcomes these problems in the prior art. An object of the present invention is to improve the signal threshold immunity with respect to process and temperature variations.
The novel circuit of the present invention features thresholds which may be programmed by means of controlling the ratio of a reference resistor to an external resistor for each input signal. Advantages of the receiver circuit of the present invention are that the signal thresholds can be outside of the supply voltage limits for the receiver circuit, and also only one resistor is required per each signal input. The receiver thresholds also have hysteresis. The present invention also makes it possible to test a receiver circuit at its input pin by forcing a voltage and observing a current. This reduces the time and complexity involved with the testing of analog parameters on a complex integrated circuit whose internal nodes cannot be directly measured.